Materials used for artificial bones, artificial dental roots, bone fillers, etc. (hereinafter referred to as “bone-filling materials”) in dentistry, brain surgery, plastic surgery, orthopedic surgery, etc. are desired to have (a) no toxicity, (b) sufficient mechanical strength and (c) excellent compatibility with biological tissues.
Because porous calcium phosphate ceramics meet these conditions, they are utilized as bone-filling materials. When used as bone-filling materials, the porous calcium phosphate ceramics preferably have as high porosity as possible from the aspect of biocompatibility. However, because higher porosity leads to lower mechanical strength in the porous bodies, they cannot be used as bone-filling materials for portions needing high mechanical strength. Thus, porous calcium phosphate ceramics having both excellent biocompatibility and mechanical strength are desired.
JP 2000-302567 A (corresponding to U.S. Pat. No. 6,340,648) discloses a sintered body comprising a skeleton portion formed by substantially dense sintered calcium phosphate, which has a finely ragged surface or a porous sintered calcium phosphate layer on the surface. JP 2000-302567 A (corresponding to U.S. Pat. No. 6,340,648) describes that fine raggedness or a porous sintered calcium phosphate layer on the surface of the porous sintered body increases a specific surface area, making it easy for osteoblasts to attach to the surface of the porous sintered body.
However, research by the inventors has revealed that to accelerate the formation of new bone, bone-filling materials should be able to trap bone-forming proteins and act as a scaffold for osteoblasts, and that it is effective for that purpose that the bone-filling materials have nanometer-order fine pores with complicated structure on the surface. Even though there are fine projections and recesses on the surface as in the sintered calcium phosphate body of JP2000-302567 A (corresponding to U.S. Pat. No. 6,340,648), such surface fails to trap bone-forming proteins sufficiently to form new bone and does not act as a scaffold for osteoblasts. It has been found that the diameters of fine pores necessary for trapping bone-forming proteins and acting as a scaffold for osteoblasts are 1 to 5000 nm. In general, sintered porous calcium phosphate does not have fine pores with completed structure, whose diameters are more than 5000 nm. Accordingly, even though there are sintered porous calcium phosphate layers on the surface as in the sintered body of JP2000-302567 A (corresponding to U.S. Pat. No. 6,340,648), the formation of new bone cannot be sufficiently accelerated.